This invention relates to a method for converting lower grade, high-melt-point uintaite into higher grade, lower-melt-point materials. The method comprises three steps. In the first step, low-grade, high-meltpoint uintaite is first dissolved in a medium polarity solvent and then blended with a nonpolar saturated hydrocarbon at a volume ratio that determines the meltpoint of the final upgraded uintaite product. In the second step, residual asphaltenes are removed from the solvent-uintaite mixture. In the third step, the solvent is separated from the asphaltene-free uintaite mixture and is recycled to produce an upgraded uintaite having a desirable meltpoint.
In particular, I have found that the proportion of nonpolar saturated hydrocarbon to uintaite solution determines the amount of asphaltenes removed and therefore the meltpoint of the resulting product. When I used a 20:1 volume ratio, all of the asphaltenes were removed resulting in a uintaite which has a meltpoint nearly 100.degree. F. below the highest grade of naturally occurring uintaite.
Uintaite is a kind of natural asphalt mined in Utah and Colorado in the United States and obtained as dark and brilliant solid in a fairly pure state. Uintaite is thought to be a thermally immature lacustrine petroleum derived from Green River shale source rock by a natural expulsion process. Uintaite has a penetration of 0-1 and a softening point of about 140.degree. C.; also, its hardness is very high. It has extremely low adhesiveness so that it can be readily pulverized into non-sticky particles. Moreover, uintaite is highly miscible or compatible with other asphalts, paint solvents, etc., and has high weather-resistance.
Researchers in the field have disclosed many methods for extracting various fractions from bituminous materials. The most well known of these is "propane extraction" in which asphaltic materials are extracted from heavy hydrocarbons by a single solvent extraction step using propane. For example, U.S. Pat. No. 2,726,192 to Kieras discloses extracting propane precipitated asphalts with n-butanol in the range of 20:1. Kieras teaches that the temperature of the extract is progressively lowered to produce the desired resin fractions.
U.S. Pat. No. 2,940,920 discloses that solvents other than propane can be used to separate heavy hydrocarbon materials into at least two fractions at a greatly improved rate of separation and in a manner which eliminates certain prior art operating difficulties encountered in the use of propane type solvents (C.sub.2 to C.sub.4 hydrocarbon solvents). That patent discloses effecting the separation by using high temperature-pressure techniques and by using pentane as one of a group of suitable solvents. Such practice permits a deeper cut to be made in the heavy hydrocarbon material, but as a consequence, more resinous bodies are present in the resulting oil fraction, tending to decrease the quality of that oil.
U.S. Pat. No. 3,830,732 discloses a two-solvent extraction process for producing three fractions from a hydrocarbon charge stock containing asphaltenes, resins and oils. The charge stock is admixed with a first solvent in a volumetric ratio of solvent to charge stock of less than about 4:1 to form a mixture that is introduced into a first extraction zone maintained at an elevated temperature and pressure. The mixture separates within the first extraction zone to produce a first solvent-rich liquid phase containing oils which are free of asphaltenes and resins and a first solvent-lean liquid phase containing asphaltenes and resins. The solvent-lean liquid phase then is contacted with a second solvent containing at least one more carbon atom per molecule than the first solvent and introduced into a second extraction zone. The second extraction zone is maintained at a lower temperature and pressure than the first extraction zone to separate the solvent-lean liquid phase into a second solvent-rich liquid phase containing resins and a second solvent-lean liquid phase containing asphaltenes.
U.S. Pat. No. 3,775,292 discloses a similar process employing a two-stage solvent extraction. There, the solvent-rich fraction which contains resins and oils is admixed with additional solvent and introduced into a second extraction zone maintained at a temperature higher than in the first extraction zone. The solvent-rich phase is separated into a second solvent-rich phase comprising oils and a second solvent-lean fraction comprising resins.
It would be desirable to provide a method in which solvent extraction can be used to convert low-grade uintaite into high-grade uintaite. Accordingly, it is the principle object of this invention to provide such a method.